It would cost about $35 million to remove the Main Street dam and remake the Scioto River through Downtown into a fertile crescent of parkland.
 
That’s the verdict of a $100,000 study city leaders and the Columbus Downtown Development Corp. commissioned last fall. The Dispatch obtained a copy of the 78-page report yesterday under the state’s open-records law.
 
The study estimates that removing the low-head dam near Main Street would cost $325,415 in 2014, less than 1 percent of the total project cost. That would reduce the Scioto River’s normal depth by as much as 7 feet and significantly narrow the stream, exposing about 33 acres of bank.
 
Making that area usable by restoring the river and its banks to a more natural state, along with building paths and parks and performing utility work — mostly extending storm-sewer outlets to the new boundaries — would account for the bulk of the cost.
 
Mayor Michael B. Coleman is serious about the idea, said Dan Williamson, his spokesman. Much as they did with the $44 million Scioto Mile, which drew $34 million in funding from noncity sources, officials are looking for partners to help with the cost.
 
“The city of Columbus could not bear the cost of this itself,” Williamson said. “This would be a city-changing project that would require partners.”
 
The Downtown Development Corp., which is leading the project, is “going through the early fundraising components,” said Amy Taylor, the group’s chief operating officer.
 
The idea isn’t just to remove the dam, it’s to remake the Scioto River Downtown, Williamson said.
 
“If you just removed the dam, that would create an eyesore,” he said.
 
Removing the dam to create new parkland along the Downtown riverfront was one of 12 proposals in a 2010 Downtown Strategic Plan. At public forums on the plan and in thousands of online comments, it was named the boldest of the proposals.
 
“People said it was the most exciting and city-changing,” Taylor said.
 
The dam, completed in 1929, does not carry utility lines across the river and is no longer needed to prevent flooding. It is now a hindrance to a healthy river, according to the report by Stantec Consulting Services and MSI Design.
 
“The Main Street Dam has slowed the flow of the Scioto River, reducing dissolved oxygen levels and inhibiting the river from transporting its sediment load,’’ the report concluded. “The dam has limited the navigability of the river, preventing boat passage and fish from migrating upstream. The Main Street Dam has assisted in creating an unhealthy environment for aquatic life.”
 
The dam is dangerous, too: People have drowned after being caught in the churning water below other low-head dams on the river.
 
The study says existing bridges along the river likely would need cosmetic aprons to cover piers exposed by the receding river, but it anticipates no structural problems for the spans. Already planned upgrades to combined sanitary and storm sewers on that stretch of the Scioto would almost eliminate spills starting in 2015.
 
Meanwhile, the narrower river would complement, not compete with, recently added Downtown parks and bridges, Williamson said.
 
The project’s biggest expense — about $20 million — would involve restoring the river channel and the river edge. That would mean sculpting the streambed along 1.2 miles of the river into a healthier, more natural series of pools and shallows.
 
Work along the banks would add native plants and habitat between the path and the river. Upslope from the path would be tended parkland.